Hi croscwa, I agree that the STEM board is equivalent and similar to the UNO, but it is not identical, I am interested in what happens when the power switch is changed to 3.3 Volts, does the whole card run at 3.3v or just the I/O pins? If it is the whole card, does it run a a slower speed? Also pins A6 & A7, are they like some Arduino's and are just floating input pins without Pull-Up resistors or are they fully functional analog I/O pins. There were the questions that came to mind when I was looking at the card, and no doubt other people will have further questions that could be answered by some documentation.
Hi again, From my tests I think that it just switches in TTL level converters for the I/O pins. You can test this yourself by connecting a voltmeter to a digital pin, load a program that sets the pin to output and sets it high, note the voltage it should be 5V, switch off the Pi-bot, and then move the switch from 5V to 3.3V and power up the Pi-Bot, your volt meter should now be reading 3.3V. To run the ATMEGA328, the processor, on the Pi-Bot, at 3.3 V would need changes to some of the settings (fuses) within the processor to prevent it powering down due to the lower voltage.
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